1. Field of the Invention
The present invention relates generally to agricultural combines for harvesting crops. In particular, the present invention relates to an improved threshing cylinder with rasp-type bars for separating grain from plant residue in a combine.
2. Description of the Related Art
A combine is an agricultural machine that harvests, threshes, and cleans grain while moving over a field. The combine typically has a complicated threshing system for separating the grain from the crop residue and a series of conveyors for depositing the grain into a holding bin and eventually into a wagon or truck. The crop residue is exhausted from the rear of the combine and deposited in the field being harvested.
Combines typically have a rotating threshing cylinder used in the early stages of grain-crop residue separation. The rotating cylinder operates in cooperation with a concave structure positioned adjacent to and below the cylinder. As the crop moves between the threshing cylinder and the concave, the cylinder-concave combination operates to separate the grain from the husk or leafy portion of the plant. The cylinder includes a plurality of rub-type bars or rasp-type bars spaced around the periphery and extending the length thereof, while the concave includes a plurality of spaced bars generally parallel to the rub-type bars or rasp-type bars. The crop is directed to the space between the rotating cylinder and the concave, and the action of the rotating cylinder upon the crop causes the grain to become separated from the remaining portion of the plant. The grain is then subjected to additional processing for further separation, while the crop residue is discharged from the combine.
Threshing cylinders can be positioned transverse to the direction of movement of the combine over the field as shown, for example, in U.S. Pat. No. 4,796,645. Alternatively, the threshing cylinder can be positioned longitudinally to the direction of flow, in which case the combine is commonly referred to as an axial-flow machine, and the threshing cylinder is referred to as a "rotor." Hybrid machines having both a transverse threshing cylinder and an axial separating unit have also been disclosed as shown, for example, in U.S. Pat. No. 5,083,977. The term "cylinder" as used in the present application is intended to cover all of the cylindrical threshing mechanisms used in these arrangements.
Conventional threshing cylinders have an "open" construction, which is shown, for example, in U.S. Pat. Nos. 3,927,679 and 5,254,036. The open cylinder construction has caused various problems during operation. For example, the impact of the open cylinder structure upon the plant often results in cracking of the grain. In addition, debris such as crop residue and soil ingested by the combine is frequently deposited in and retained by the rotating cylinder. As the mass of this debris increases, out of balance operation of the cylinder occurs resulting in irregular engagement of the crop by the cylinder and degraded grain separation. This out-of-balance condition may require the combine operator to interrupt operation and clean out the debris within the cylinder. This condition also causes increased wear on the cylinder's bearings resulting in reduced combine reliability.
Enclosed threshing cylinders have been developed, in part, to overcome the problems experienced with open cylinder constructions. An enclosed cylinder construction is shown, for example, in U.S. Pat. No. 4,796,645. Enclosed cylinders generally have a solid, continuous cylindrical surface on which cylinder bars are mounted for threshing the grain. Alternatively, the enclosed cylinder structure can have a star or polygonal-shaped cross-section as shown, for example, in the Fall 1994 Edition of the Semi Annual Buyers Guide for KS/NE Farmers & Breeders and marketed under the proprietary name "Sunnybrook High Inertia Rotors." The enclosed cylinders are closed on their ends so that crop material and other debris are kept out of the middle of the cylinder during operation.
Cylinder bars for combines are of three basic types: rasp-type bars, flat rub-type bars, and angled rub-type bars. The terms "rasp-type bar" and "rub-type bar" are terms of art that have a definite meaning to those skilled in the art. However, it is noted that certain patent disclosures in this technology, such as U.S. Pat. No. 4,796,645, have used the term "raspbar" to refer to a structure that those skilled in the art would normally refer to as an angled rub-type bar. The differences between these basic types of cylinder bars will become apparent from the following descriptions thereof.
Flat rub-type bars were used in older combines and had a relatively flat configuration with a relatively wide spacing and a short, curved tooth configuration. The flat rub-type bars had a fairly thin base and, consequently, had very little strength for holding threshing cylinder elements in their proper places. The flat rub-type bars required backing plates for mounting, which were permanently affixed to the cylinder elements, usually with rivets, in order to maintain permanent alignment of those parts, and to avoid bending of cylinder bars. Backing plates, however, were built in a low, narrow profile, which in conjunction with shorter teeth on the cylinder bar required a relatively fast cylinder speed to feed the machine. Also, the short profile tended to scoop material into the cylinder, causing balance problems.
Angled rub-type bars, which are widely used today have a shape that is much more rigid than the conventional flat rub-type bars, and can be mounted directly to the cylinder components without a backing plate for reinforcement. Angled rub-type bars, such as those shown in U.S. Pat. No. 4,796,645, are bent at an angle of approximately 45 degrees between a shallow-toothed portion and a flat leading face. The flat leading face is approximately 1 1/4 inch wide and has mounting holes formed therein for securing the rub-type bars to mounting structures on the cylinder. The angled rub-type bars are mounted on the cylinder with a forward pitch of approximately 15 degrees to allow maximum exposure to the most efficient feeding area of the tooth curvature. Since a maximum height of the teeth is approximately only 5/16 inch when they are new, the flat leading face assists in feeding material through the machine. Moreover, the wider leading profile, as opposed to an original flat rub-type bar and backing plate combination, helps to prevent material from entering the interior of the cylinder.
Angled rub-type bars operate in the following manner. The front face, at an approximately 55-degree angle to the concave crossbars, gathers material and pulls it across the concave for threshing. This leading angle gives material a rolling action, and forces the smaller portions to a pinch point between the top radius of the cylinder bar teeth and the concave crossbars. At this point, the material is spread into a thinner layer than was originally carried into the machine. The teeth on the outer surface of the cylinder bar are provided to comb through and move this thinned layer, and also to provide an escape channel for grain that would otherwise be broken or crushed. Although initial impact of the cylinder bar face will cause some threshing, virtually all of the threshing and separating functions are provided by the resistance of the concave crossbars to the material being forced over them. It is therefore critical that as much material as possible be moved to the outer periphery of the cylinder, and that the teeth be maintained as near to full height and original curvature as practicable.
Several problems have been observed with angled rub-type bars, including overthreshing, poor separation, cracking, underthreshing, inconsistent cylinder speed, and bending and twisting under load. The overthreshing occurs because the material is separated in a thin layer, and larger components of the crop are forced to the concave crossbars where they are torn up and forced to the cleaning shoe. Also, in order to spread the material as it enters the threshing area, a relatively fast cylinder speed is required.
Poor separation of the angled rub-type bars occurs because some grain is not carried to the outer periphery of the cylinder and rests against the cylinder bar face or remains mixed with dunnage. This grain must be separated in the secondary separation area. Cracking occurs because the dunnage is torn into relatively small pieces by the angled rub-type bars and falls through the chaffer more easily and requires closing down the cleaning sieve. This causes more grain to be returned to the cylinder area, where it is dropped onto the concave without benefit of the padding effect of the husks, straw, and so forth.
Underthreshing of the angled rub-type bars occurs in larger grains, where the size or amount of material entering does not allow the load to be thinned adequately for separation by the cylinder bar teeth against the concave crossbars without grinding. Inconsistent cylinder speed occurs in weedy situations or vine crops because the smooth front face of the angled rub-type bar occasionally fails to pull material from the feeder house chain. This material tends to pile in front of the concave, eventually moving through in a large mass, causing an extra load for the cylinder drive components. Occasionally, this mass will lodge and cause complete stoppage of the cylinder. The bending and twisting under load occur in conventional machines that use cylinder spiders that float on the center shaft of the cylinder. This arrangement eases alignment for purpose of installation, but also allows the bars to flex and sometimes remain in a bent or twisted shape if the machine is slugged. If the angled rub-type bars are heat treated, they also occasionally break due to metal fatigue caused by this flexing.
In contrast to the flat and angled rub-type bars, rasp-type bars use a tall, aggressive tooth configuration, with a relatively close spacing between the teeth. The rasp-type bars use a tooth configuration which is approximately twice as tall as the teeth on an angled cylinder bar. The leading side of these teeth is at an angle of about 75 to 80 degrees relative to a tangential line on the path of rotation (i.e., about 10 to 15 degrees relative to a radial line passing through the center of rotation). The rasp-type bars typically have a spacing between the teeth of approximately 1/4 inch with an arch in the top center of the tooth that approximately conforms to the concave bore. The base of the rasp-type bars is fairly thick and heavy, and usually conforms to a cylinder spider that has a circular mounting rim. The rasp-type bars are typically built heavy enough to be mounted independently, and strong enough to hold floating cylinder heads (i.e., spiders) in proper alignment when bolted directly to them. As compared to the flat and angled rub-type bars, the rasp-type bars have several advantages, which will be described below in conjunction with the present invention. However, prior to the Applicant's invention, rasp-type bars were not used in conjunction with an enclosed cylinder structure.